Thiophene chemistry and the chemical stability of the thiophene ring hold potential for use of thiophene materials in molecular-based electronics and photonics. In particular, xcex1xcex1xe2x80x2-conjugated thiophene oligomers (nTs) and polymers (polythiophenes-PTs) have attracted great interest as semiconducting elements in organic thin-film transistors (TFTs).[1,2,] To be useful in such devices and related structures, the 
organic material must support a channel of holes or electrons (p- or n-type semiconductor, respectively) created by the gate electrode bias, which switches the device xe2x80x9conxe2x80x9d. Furthermore, the charge mobility of the material must be sufficiently large to increase the source-drain on-conduction by many orders of magnitude over the xe2x80x9coffxe2x80x9d state. The density of the charge carrier in the channel is modulated by voltage applied at the gate electrode.
To date, the most noteworthy examples of this family of compounds are unsubstituted, xcex1,xcfx89- and xcex2,xcex2xe2x80x2-dialkylsubstituted nT (n=4,6), and xcex2-alkylsubstituted PT, where optimized carrier mobilities (0.1-0.6 cm2 Vxe2x88x921 sxe2x88x921) and on/off ratios ( greater than 106) approach those of amorphous silicon.[1e,2a,c,e,3] However, without exception, these systems facilitate hole injection and behave as p-type semiconductors, presumably because the thiophene electron-richness renders negative carriers susceptible to trapping by residual impurities such as oxygen[4]. Even so, increasing the number of thiophene units decreases dramatically environmental (air, light) stability and causes processing and purification difficulties.
Electron transporting (n-type) organic materials are relatively rare. However, developing/understanding new n-type materials would enable applications[5] such as bipolar transistors, p-n junction diodes, and complementary circuits as well as afford better fundamental understanding of charge transport in molecular solids. The major barrier to progress however, is that most n-type organics are either environmentally sensitive, have relatively low field mobilities, lack volatility for efficient film growth, and/or are difficult to synthesize.[5e,6,7]
As indicated by the foregoing notations, these and other aspects of and teachings of the prior art can be found in the following:
[1] (a) G. Horowitz, F. Kouki, A. El Kassmi, P. Valat, V. Wintgens, F. Gamier, Adv. Mater. 1999, 11, 234. (b) F. Gamier, R. Hajaoui, A. El Kassmi, G. Horowitz, L. Laigre, W. Porzio, M. Armanini, F. Provasoli, Chem. Mater. 1998, 10, 3334. (c) X. C. Li, H. Sirringhaus, F. Gamier, A. B. Holmes, S. C. Moratti, N. Feeder, W. Clegg, S. J. Teat, R. H. Friend, J. Am. Chem. Soc. 1998, 120, 2206. (d) G. Horowitz, F. Kouki, F. Gamier, Adv. Mater. 1998, 10, 382. (e) L. Antolini, G. Horowitz, F. Kouki, F. Garnier, Adv. Mater. 1998. 10, 381. (f) G. Horowitz, Adv. Mater. 1998, 10, 365.
[2] (a) W. Li, H. E. Katz, A. J. Lovinger, J. G. Laquindanum, Chem. Mater. 1999, 11, 458. (b) H. E. Katz, J. G. Laquindanum, A. J. Lovinger, Chem. Mater. 1998, 10, 633. (c) J. G. Laquindanum, H. E. Katz, A. J. Lovinger, J. Am. Chem. Soc. 1998, 120, 664. (d) T. Siegrist, C. Kloc, R. A. Laudise, H. E. Katz, R. C. Haddon, Adv. Mater. 1998, 10, 379. (e) H. E. Katz, J. Mater. Chem. 1997, 7, 369. (f) A. Dodalabapur, L. Torsi, H. E. Katz, Science 1995, 268, 270.
[3] (a) H. Sirringhaus, P. J. Brown, R. H. Friend, K. Bechgaard, B. M. W. Lengeveld-Voss, A. J. H. Spiering, R. A. J. Janssen, E. W. Meijer, P. Herving, D. M. de Leeuw, Nature 1999, 401, 685. (b) G. Barbarella, M. Zambianchi, L. Antolini, P. Ostoja, P. Maccagnani, A. Bongini, E. A. Marseglia, E. Tedesco, G. Gigli, R. Cingolani, J. Am. Chem. Soc. 1999, 121, 8920. (c) J. H. Shon, C. Kloc, R. A. Laudise, B. Batlogg, Appl. Phys. Lett. 1998, 73, 3574.
[4] Handbook of Heterocyclic Chemistry; A. R. Katritzky Ed.; Pergamon Press: Oxford, 1983.
[5] (a) Y. Y. Lin, A. Dodabalapur, R. Sarpeshkar, Z. Bao, W. Li, K. Baldwin, V. R. Raju, H. E. Katz, Appl. Phys. Lett. 1999, 74, 2714. (b) G. Horowitz, Adv. Mater. 1998, 10, 365. (c) A. Dodalabapur, J. G. Laquindanum, H. E. Katz, Z. Bao, Appl. Phys. Lett 1996, 69, 4227. (d) N. C. Greenham, S. C. Moratti, D. D. C. Bradley, R. H. Friend, Nature 1993, 365, 628. (e) S. Sze, Semiconductor Devices Physics and Technology; Wiley: N.Y., 1985; p. 481.
[6] (a) C. P. Jarret, K. Pichler, R. Newbould, R. H. Friend, Synth. Met. 1996, 77,35. (b) R. C. Haddon, J. Am. Chem. Soc. 1996, 118, 3041. (c) G. Horowitz, F. Kouki, P. Spearman, D. Fichou, C. Nogues, X: Pan, F. Gamier, Adv. Mater. 1996, 8, 242. (d) J. G. Laquindanum, H. E. Katz, A. Dodalabapur, A. J. Lovinger, J. Am. Chem. Soc. 1996,118, 11331.
[7] The transport properties of metal/xcex1,xcfx89-dicyano-6HT/metal structures are highly metal/interface-dependent; TFT carrier signs and mobilities have not been reported: F. Demanze, A. Yassar, D. Fichou, Synthetic Metals 1999, 101 620.
As shown from the above discussion, there are a considerable number of problems and deficiencies associated with the prior art relating to useful organic n-type semiconductor compounds, compositions and/or materials, including those discussed above. There is a demonstrated need for such materials, compositions, layers and/or composites for thin film deposition and related applications useful in conjunction with the fabrication of thin film transistors and related devices as can be incorporated into an integrated circuit.
Accordingly, it is an object of the present invention to provide new and useful n-type organic materials, together with one or more methods of preparation, overcoming those various shortcomings and deficiencies of the prior art.
It will be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can meet certain other objectives. Each objective may not apply equally, in all instances, to every aspect of the present invention. As such, the following objects can be viewed in the alternative with respect to any one aspect of the present invention.
It is another object of the present invention to provide a facile, efficient synthetic method for the preparation of an n-type thiophene conductive material, such preparation resulting in high yield and purity of the desired thiophene material.
It is yet another object of the present invention to provide n-type semiconducting thiophene compounds and related materials and/or thin films which can be used in the fabrication of and in conjunction with a variety of circuitry related devices, including, but not limited to, diode, bipolar junction transistor and field-effect transistor (either junction or metal-oxide semiconductor) devices
It is yet another object of the present invention to provide for the synthetic. modification of organic semiconductive molecular solids to alter electronic behavior, in particular the use of such modified thiophenes to provide and facilitate electron transport.
Other objects, features, benefits and advantages of the present invention will be apparent from the foregoing, in light of the summary and the examples and descriptions which follow, and will be readily apparent to those skilled in the art having knowledge of various semiconducting materials, their preparation and subsequent use. Such objects, features, benefits and advantages will be apparent from the above as taken in conjunction with the accompanying examples, tables, graphs, data and all reasonable inferences to be drawn therefrom.
In accordance with one aspect of the present invention, one or more of the foregoing objects can be achieved by use of one or more of the thiophene compounds, compositions and/or materials of the type described herein, and/or with a suitable substrate material as part of a composite or a device incorporating such a composite.
In accordance with another aspect of the present invention, one or more of the preceding objects can be achieved with a method described herein, including the use of a thiophene material as an n-type semiconductor to transport electrons.
In accordance with another aspect of the present invention, one or more of the foregoing objects can be achieved with an organic thin film transistor device which includes a source electrode, a drain electrode and a semiconductor material between the electrodes, the material preferably comprising an n-type fluoroalkyl-substituted polythiophene composition.
In accordance with yet a further aspect of the present invention, a method is provided by way of using introduction of substituents to a semiconducting composition to alter charge conduction there through, such that a material which would otherwise be considered a p-type conductor becomes an n-type conductor through a synthetic transformation of the type described herein. Various other properties such as band gap (expansion), electron mobility (increased), electron affinity (increased) and ionization potential (higher) are similarly altered.
The present invention includes the first n-type thiophene semiconductor compositions and/or materials, for use with a variety of applications or devices including, but not limited to, organic TFTs. A preferred thiophene composition/material comprises xcex4,xcfx89-diperfluorohexylsexithiophene 
designated as DFH-6T, shown above and as structurally compared to the sexithiophene (6T) and dihexylsexithiophene (DH-6T) compositions of the prior art. Fluoroalkyl functionalization of a thiophene core significantly alters the electronic, film growth, and semiconducting properties of the resulting films.
The present invention contemplates, in part, a range of fluoroalkylated compositions and/or materials including the corresponding fluoroalkylated olio- and polythiophene compositions. Fluoroalkylation includes various alkyl chain lengths and fluoro-substitutions thereof, such as would result in an alteration to n-type semiconductivity, as compared to p-type conductivity of the unaltered composition. Similar effects can be achieved by introduction/insertion of electron deficient moieties, such as fluoro- and perfluoroaryl groups and various heterocycles. Known synthetic procedures can be used or modified as would be known to those skilled in the art made aware of this invention to provide a variety of thiophene cores, each with the appropriate insertions and/or fluoroalkyl substituents. However, for purposes such as processing and subsequent device fabrication, a preferred core has about 4-7 conjugated thiophene units. Likewise, C5-C7 fluoroalkyl substitution is preferred and can be accomplished using commercially-available reagents, but various other substitutions can be achieved through synthesis of the corresponding fluoroalkyl compounds. Thiophene core substitution and heterocycle insertion is, therefore, limited only by the desired degree of n-type semiconductivity.
A TFT device with, for instance, a DFH-6T active layer operates in the n-type accumulation mode, indicating DFH-6T and other such thiophene compounds are n-type conductors. Compared to prior art materials such as DH-6T and 6T, the new fluorinated thiophenes of this invention are significantly more chemically and thermally inert, and can be transported quantitatively into the vapor phase without decomposition. In the solid state, the inventive thiophene units have strong xcfx80-xcfx80 intermolecular interactions. As described below, film growth morphologies can depend on growth temperature and substrate pretreatment and/or functionalization.
This invention demonstrates that fluoroalkyl functionalization of a thiophene core substantially enhances thermal stability, volatility, and electron affinity vs. the non-fluoro analogs and affords the first n-type thiophene for use, as an example, in a TFT. As a representative material of this invention, DFH-6T film morphology is sensitive to substrate temperature and surface pretreatment, with crystallite size increasing with increasing growth temperature. UV-vis/PL and XRD studies indicate that while DFH-6T has close intermolecular xcfx80-stacking, it is not isostructural with the DH-6T analog. Since thiophene oligomers of the prior art are typically p-type, the present invention using n-type semiconductors can provide a pathway by which an all-thiophene complementary circuit can be realized.
In accordance with the preceding, the present invention further includes thiophene systems such as those represented by general structural formulas 1-3, as can be prepared in high yield via palladium(0)-catalyzed coupling of haloaromatics with stannyl (Stille coupling) and Grignard reagents.
One embodiment of this invention includes various prefluoroalkyl and/or fluoroalkyl substituted thiophene oligomers or polymers, as can be represented by the structural formula 
wherein R1, R2 and R3 are selected from the substituent group consisting of fluoroalkyl moieties, CnH2n+1 and where n is about 1-12, H, F and (CH2)aX and where a is about 1-12 and X is selected from the group consisting of amino, hydroxy and carboxylic acid functionalities; and x, y and z are integers from the group of integers consisting of 0 and integers greater than 0.
The fluoroalkyl moieties of such compositions can include but are not limited to the corresponding linear, branched and/or cyclic substituents, optionally in the presence of one or more alkyl and/or fluorine substituents. Alternatively, an alkyl substituent can further include a functional group including but not limited to those described in Examples 14 and 15, below, such that the resulting polythiophene composition can be further transformed and/or modified. Various other functional groups will be well known to those skilled in the art and made aware of this invention, as will be the corresponding synthetic techniques/procedures by which to effect such a transformation or polythiophene modification.
With respect to the aforementioned fluoroalkyl moieties, various properties of such compositions can be modified by alkyl length and extent of alkyl fluorination. Preferred compositions can include those with a fluoroalkyl moiety having the compositional formula CnF2n+1, where n is about 1-8. The compositions of such embodiments can be further modified by choice of integers x, y and z. Regardless of substitution, such preferred embodiments can also include those in which x is about 0-4, y is about 0-8 and z is about 0-12. However, it should be understood, in the broader context of this invention, that the composition of such polythiophenes and the number of conjugated thiophene units is limited only by synthetic technique.
Representative structures include but are not limited to the following: 
Compositions 1a-h were prepared according to Schemes 1 and 2. (See, also, Examples 17 and 17a-g.) 
Another embodiment of this invention includes various xcfx80-conjugated perfluorophenyl-thiophene oligomers, as can be represented by the structural formula 
wherein R1, R2 and R3 are selected from the substituent group consisting of fluoroalkyl moieties, CnH2n+1 and where n is about 1-12, H, F, and (CH2)aX and where a is about 1-12 and X is selected from the group consisting of amino, hydroxy and carboxylic acid functionalities; and x, y and z are integers selected from the group of integers consisting of 0 and integers greater than 0.
The compositions of this embodiment and the chemical/physical properties corresponding thereto, can be modified as described above by choice and extent of thiophene substitution. In addition, as the present embodiment illustrates, the compositions of this invention can be further modified by insertion of perfluoroaryl components between conjugated thiophene units. Use thereof in combination with any of the aforementioned substitution parameters can provide a route to choice and design of compositions with specific electronic properties.
Representative structures include but are not limited to the following: 
Compositions 2a-b were prepared according to Scheme 3. (See, also, Examples 18a-e.) 
Another embodiment of the present invention includes various xcfx80-conjugated electron-poor heterocycle (including azine)-thiophene oligomers, as can be represented by the following structural formula 
wherein R1, R2 and R3 are selected from the substituent group consisting of fluoroalkyl moieties, CnH2n+1 and where n is about 1-12, H, F. and (CH2)aX and where a is about 1-12 and X is selected from the group consisting of amino, hydroxy and carboxylic acid functionalities; x, y and z are integers selected from the group of integers consisting of 0 and integers greater than 0; and A, B, W and Z are selected from the group of moieties consisting of N and CH:
Modification of a polythiophene composition can also be achieved through insertion of a suitable heterocyclic component, the effect of which can be comparable to perfluoroaryl substitutions of the sort described above. Several such insertions are illustrated, below, but this embodiment can be extended to include other electron-deficient heterocycles including but not limited to thiadiazine and tetrazine. Polythiophene compositions including such components can be prepared through straight-forward extensions of the general synthetic techniques described herein, such extensions as would be understood by those skilled in the art. The electronic effect afforded such thiophene compositions by heterocycle insertion can be further tailored for a specific end-use application through choice and degree of substitution, as described more fully above. Accordingly, as with the preceding fluoroalkyl and perfluoroaryl compositions, the heterocyclic compositions of this embodiment can vary without limitation corresponding to substituent (R1, R2 and R3), optional functional group (amino-, hydroxy- or carboxylic acid groups), heteroatom identity and/or number of thiophene and/or heterocyclic units.
Accordingly, as also described elsewhere herein, the present invention can further include a method of using thiophene structural modification to provide, promote and/or enhance n-type thiophene conductivity. Such a method includes (1) preparing a polythiophene composition having a plurality of conjugated thiophene components or moieties; (2) providing the composition a structural modification sufficient to promote n-type conductivity, such a modification selected from the group of structural modifications described above and including but not limited to fluoroalkyl substitution, fluorine substitution, fluoroaryl insertion, heterocycle insertion and combinations thereof. As described herein and as would be understood to those skilled in the art, such modifications can be made or provided en route to the preparation of such polythiophene compositions. Alternatively, various synthetic techniques, depending upon the desired modification, can be made subsequent thereto. Such modifications can provide a wide variety of polythiophene compositions, commensurate with the broad scope of this invention, such compositions including but not limited to those embodiments discussed above.
Representative structures include but are not limited to the following: 
Compounds 3a-d were prepared according to Scheme 4. (See, also, Examples 19a-f). 